Homologous Traits:
Whale flippers are homologous to human arms. Whales, as well as humans, are considered mammals. Most people would not guess this of whales considering they are sea creatures. Whales unlike fish maintain an internal body temperature. Their ears contain three small bones used for processing vibrations. Unlike whales, humans are quite obviously land mammals. We share many of the same traits such as being warm blooded, live birth, and growing hair.
The homologous trait contained in humans and whales is located in the human arm and in the whale flipper. The whale flipper provides the whale with the resources it needs to be able to glide smoothly and quickly through water. Certain species of whales even use their flippers to help them hunt their prey. Whale flippers contain only slight differences from the human arm. The radius of the whale flipper is much smaller than that of the human arm. The human arm as well as the whale flipper both contain a humerus. However, the humerus of the whale flipper contains a slight, smooth arch, where as the human humerus contains a much deeper arch. Human phalanges are significantly shorter and more proportionate to one an other where on the other hand, the phalanges contained in the whale flipper are three short phalanges accompanied by two longer ones. The bone structure of the whale's flipper (shown to the right) is significantly different from the structure of the human arm (shown below to the left) in that the human arm is much longer and thinner than the flipper of the whale. There are also differences in the shape of the bones themselves as well as in the size of the bones and the spacing between them as previously described above. 
The common ancestor of the two species is a placental mammal such as a small insect eater. This ancestor possessed the same homologous trait as the two listed above. The species previously described are also placental mammals, meaning that they nourished their young in the womb by sharing oxygen and nutrients. Analogous Traits:
Penguins and fish are analogous to one another based upon a fish's fin structure and a penguin's fin-like structure. Penguins use their fins to help them navigate through the arctic conditions in which they live including water. Fish use their fins to navigate through only water. The fins of penguins can also be considered wings seeing as penguins are birds.
The common ancestor of penguins and fish did not posses the analogous trait. This is because the analogous trait is not passed through ancestral lineage. These species developed these traits based upon their environmental demands where as the species listed above in the homologous explanation received their traits from their ancestors.
Sources: http://education-portal.com/academy/lesson/analogous-structures-definition-examples-quiz.html
Hey, i really liked your blog post this week. The two species you picked to show homologous traits were good examples. Whales and humans are very different and you clearly explained how our arm structures are the same. I also enjoyed your analogous trait example, and i actually picked the same species. You did a good job of answering all the questions. I learned a lot by reading your blog. Good job.
ReplyDeleteHi Elizabeth,
ReplyDeleteYour blog was very well done.I actually chose similar homologus species, mine being a dolphin flipper and human arm. The information you provided was well thought out and very nicely put together. Your anologous species were also very interesting to read about! Great job!
Great background information and detail for your homologous pairing. You did well explaining the ancestry of the trait as well.
ReplyDelete"It is obvious that the two are analogous because one is a bird and one is a fish..."
Actually, not so obvious. Birds and fish are both vertebrates and possess many homologous traits. The gill branches in fish are actually homologous to many structures in amphibians, reptiles, birds and mammals, such as the inner ear bones. Just because they are different in appearance, you can't automatically deduce lack of relatedness. That is one of the lessons you are supposed to learn from this assignment!
In order to understand whether or not a set of traits or analogous or homologous, you have to confirm the ancestry. In the case of fish and penguin fins, what do we know about bird evolution that would help us confirm that bird wings (and penguin fins) evolved independently from fish fins?